The present invention relates to electric contact devices which slide between two parts which move relative with to each other, a first one of said parts bearing at least one multifilament brush formed of a bundle of endless wires held at one of its ends in the first part and at its other end bearing against at least one contact zone arranged on the second part.
Sliding electric contacts are found in most electrical engineering installations both in the form of wiper shoes and in combination with collector rings or collectors of rotating machines. In the early rotating machines, the wire contactors now call brushes, have been replaced everywhere by metalgraphite or electrographite brush systems. These latter devices have their well-known limitations with respect to the current density which they can transmit, with respect to the amount of contact potential difference and the problems related to friction and wear, particularly when the speed of travel is high.
The contact pressure necessary for metallographitic brushes and the phenomena appearing at the interface between them and the contact zone of the associated rotating part have up to now limited their use to a normal or preferably inert atmosphere, preventing their use in more hostile gaseous environments and particularly in liquids.
Now the solution of this problem of immersion would satisfy very many demands. Thus, with respect to hostile gaseous conditions, the contact shoes of railway motor cars very frequently become unusable as a result of constant precipitation or due to the persistence of thick saline fogs. As for electric motors and more particularly dc motors, they rapidly prove very limited, particularly because of problems associated with brush pressure, both in aeronautics when a certain ceiling must be exceeded, and when submerged where, almost exclusively for the brush-collector subassemblies, thick-hull structures resistant to pressure must be provided, and the problems in tightness resulting therefrom must be resolved.
With a motor which is capable of operating while immersed, a thin hull enclosure, placed under equipressure, would make it possible to solve most of the structural problems and those inherent with tightness, thus permitting important developments for small auxiliary motors for equipment of submarine vehicles or underwater drilling installations. Finally, for simple matters of optimal location and utilization of available space it will be understood that the possibility of immersion, for instance of a fuel pump in an airplane wing tank, as well as in a car fuel tank, would afford very great advantages.
The conventional metallographitic or electrographitic brushes as stated above must be used in relatively controlled atmospheres and, differing from other turning parts of electrical machines encounter, when immersed in a liquid medium, almost insurmountable difficulties related to the pressure to be applied to the brushes in order to counteract the lifting force created by the "oil wedge" below the brushes and the related phenomena of electro-erosion which very rapidly make these conventional brushes ineffective.